cancel
Showing results for 
Search instead for 
Did you mean: 

Spark Plug

gleneagles
Community Veteran
Posts: 10,714
Thanks: 2,224
Fixes: 16
Registered: ‎02-08-2007

Spark Plug

How long does a spark plug continue to work effectively in a 4 stroke engine ?

Nope I am not talking about spark plugs in your car, the user manual or internet is full of such information.

 

What I am referring to is the spark plug in a lawnmower 100cc engine.

 

The manual says 100 hours and it would seem...quite accurate.

 

Cleaned and regapped more car spark plugs than I care to remember but having done the same with the one in the mower it  still refused to fire up, replaced plug with a new one and it worked first time. At £3.95 on eBay hardly worth the effort of cleaning a old one but I am puzzled why these plugs have such a limited life considering they are not much smaller than a standard spark plug.

We are born into history and history is born into us.
20 REPLIES 20
Strat
Moderator
Moderator
Posts: 30,409
Thanks: 3,357
Fixes: 506
Registered: ‎14-04-2007

Re: Spark Plug

I've had my petrol mower for quite a few years with the same plug.

I did remove it a couple of years ago but it looked ok so I put it back.

It might benefit for a new plug but it runs ok so I leave it, just checking the oil level which hardly changes.

Customer and Forum Moderator. Windows 10 Firefox 88.0.1 (64-bit)

shutter
Community Veteran
Posts: 20,829
Thanks: 3,186
Fixes: 47
Registered: ‎06-11-2007

Re: Spark Plug

Probably, cos it runs at a much higher temperature?  and the ceramic resistance breaks down ? or the internals, get shook about so much that a disconection internally happens due to expansion and contraction properties of the ceramics and the metal interior...

 

Did you try it after replacing it with a new one ?  just to see if it was faulty  ?

 

idonno
Aspiring Champion
Posts: 1,388
Thanks: 461
Fixes: 6
Registered: ‎22-10-2015

Re: Spark Plug

@gleneagles Like you say, bargain of a price. The joys of spark plugs. As mentioned, maybe higher running temperatures does them in, although there are different grades of spark plugs.

 

What does the spark plug look like when you take it out. Sooted up would mean the mixtures too rich. Although I haven't used a recent 4 stroke mower (are they fuel injected nowadays), my 2002 4 stroke rotavator was still on its 1st spark plug when it got sold 7 years later. Cars are usually fuel injected now whereas I suspect your mower might well have a carb. Then of course the fuel goes off - supposedly. And to top it all, it doesn't get run much anyway.

 

Something to try, buy a can of Easystart. I can guarantee it will start anything as long as there is a spark - but don't use it on a turbo!

Ever helpful. Grin Sure, I’d love to help you out. Now which way did you come in?
PowerLee
Pro
Posts: 740
Thanks: 86
Fixes: 2
Registered: ‎12-03-2013

Re: Spark Plug

Most modern petrol injected cars also run a wasted spark ignition system.

The plug is also fired on the exhaust stroke which helps keep the plug at a constant operating temperature which in turn helps keep the firing tip clean.

twocvbloke
Community Veteran
Posts: 6,399
Thanks: 1,781
Fixes: 3
Registered: ‎06-11-2014

Re: Spark Plug

At 100cc, I'm guessing a Mountfield RS100 engine perchance? Though that said, most of the cheap small mower engines come with some pretty awful quality plugs, I tend to just whip 'em out and stick an NGK plug in its' place, better to use a known brand than mystery cheap special made in youknowhere... 😂

 

As for why they wear out, well in aircooled engines at least they run a lot hotter than a watercooled engine, so if they're cheaply made, they'll fail a lot sooner than a decent brand, no amount of cleaning would fix them, they're cheap tat through and through...

wotsup
Seasoned Champion
Posts: 1,809
Thanks: 1,341
Registered: ‎21-11-2018

Re: Spark Plug

I know Briggs and Stratton small mower engines are weird and wonderful things.

They seem to be a 2 stroke engine with a wet sump like a 4 stroke,  their carburettor

is a strange and simple device that runs on rubber diaphragm and springs and once

it starts to misbehave you may as well get a new one ( about £25 ) -

as for spark plugs even though my present mower is not old the plug is always black

when I take it out,  but it keeps running.  The engine kill switch shorts out ignition coil

when you release the safety handle and if the contacts on kill switch get crudded up

it can stop the spark happening all the time).

 

Made the mistake years ago and tilted the mower the wrong way ( so carburettor

was lowest point ) and oil exited through carb and soaked the foam filter ). As the video

says only tilt mower with either plug or carby up..

 

https://www.youtube.com/watch?v=Cpr9b0Qyfds

 

 

twocvbloke
Community Veteran
Posts: 6,399
Thanks: 1,781
Fixes: 3
Registered: ‎06-11-2014

Re: Spark Plug


@wotsup wrote:

I know Briggs and Stratton small mower engines are weird and wonderful things.

They seem to be a 2 stroke engine with a wet sump like a 4 stroke


 

It's like a 4-stroke because, erm, it IS a 4-stroke, don't think Briggs have ever made a 2-stroke, at least not within the past 70 years... 😂

 

As for that type of carburettor, it's a diaphragm type, and you can get rebuild kits for them cheaper than a whole carb, easily swapped in less than half an hour (give or take for cleaning up any schmoo from old, dirty or waterlogged (cos of ethanol poisoning) petrol), but at least modern Briggs engines, like the 575EX on my mower (soon to be swapped with a Honda GCV160, cos more horsepower & torque) have more "normal" carburettors, just made out of plastic which deals with the annoying corrosion problems of the older carbs, but takes away any adjustability without taking a micro drill bit to the jets...

PowerLee
Pro
Posts: 740
Thanks: 86
Fixes: 2
Registered: ‎12-03-2013

Re: Spark Plug

Was never a fan of Briggs & Stratton engines when I was in the trade, always used to bin Champion the wonder plug & replace it with a NGK.
The non adjustable plastic carburetor some where fitted with was also another wonderful piece of design.

Honda GC / GCV isnt a bad engine but I prefer the older GX series as there pretty bomb proof - oil alert sensor can fail but easily bypassed as there a pig to change sensor on as you need to split engine case in half.

Tecumseh where a decent engine, changed an oil alert sensor on one - easy swop as undo 4 bolts & sensor drops straight out the bottom.
twocvbloke
Community Veteran
Posts: 6,399
Thanks: 1,781
Fixes: 3
Registered: ‎06-11-2014

Re: Spark Plug


@PowerLee wrote:
Honda GC / GCV isnt a bad engine but I prefer the older GX series as there pretty bomb proof - oil alert sensor can fail but easily bypassed as there a pig to change sensor on as you need to split engine case in half.

 

Only trouble with the GX line is they're not that good for a push mower, given they're Horizontal shaft engines, though there were GXV models, they're not as easy to come by these days... 😁

 

Plus I got the GCV160 for a good price, so I'm happy, hopefully it'll do better than the Briggs 5.5 Intek I got a few years back, in that the Honda will run, unlike the Intek, which has not run to date...

wotsup
Seasoned Champion
Posts: 1,809
Thanks: 1,341
Registered: ‎21-11-2018

Re: Spark Plug

Got it - they are sidevalve 4 stroke - no wonder power to cc / weight is so low.  Still don't understand how oil from sump can get into carb though if you tilt engine the wrong way

https://www.youtube.com/watch?v=okNchZghrdQ

twocvbloke
Community Veteran
Posts: 6,399
Thanks: 1,781
Fixes: 3
Registered: ‎06-11-2014

Re: Spark Plug


@wotsup wrote:

Still don't understand how oil from sump can get into carb though if you tilt engine the wrong way


 

Oil can escape the engine crankcase through the PCV (Positive Crankcase Ventilation) valve which has a tube between said valve and the air filter, the idea being that gases vented from the engine, such as oil vapour and exhaust gases that get by the piston rings, get recirculated into the combustion cycle to burn them off, of course over-filling with oil or tipping the engine over so that oil gets into the valve results in it flowing out into the air filter and carb... 🙂

gleneagles
Community Veteran
Posts: 10,714
Thanks: 2,224
Fixes: 16
Registered: ‎02-08-2007

Re: Spark Plug

It’s a mountfield RS100, it has a carburettor.

Plug was fairly black and full of gunge after 2 years of use, no amount of cleaning would get it to work, replaced with new NGK plug and it fired up first time and ran fine, must admit the petrol is likely 18 months old.

Like a car it runs on 97 octane but it is possible to get 95 octane wonder if it worth buying that just for the mower.

Thanks for the interesting replies.

We are born into history and history is born into us.
twocvbloke
Community Veteran
Posts: 6,399
Thanks: 1,781
Fixes: 3
Registered: ‎06-11-2014

Re: Spark Plug

Was a good guess at it being an RS100, have one myself (not technically mine, belongs to the uncle's landlord), nice little engine, naff all power for a meadow of a "lawn" though... 😂

 

As for fuel, no point buying higher octane fuel, they're not tuned to run on it so not seeing the benefit (aside from some of the 97 coming without ethanol, which makes the fuel last longer, but definitely not 18 months!!), I'd also suggest using fuel stabiliser if keeping the fuel around for over a year, this keeps it good for a longer, not great, but stops waste at least... 🙂

Champnet
Champion
Posts: 1,676
Thanks: 537
Fixes: 7
Registered: ‎25-07-2007

Re: Spark Plug

Any recommendations for a cordless electric mower ?